Soluble anionic polymerization initiators and products therefrom

ABSTRACT

An acyclic alkane soluble anionic polymerization initiator includes a mixture of from about 90 to about 10 parts by weight of a lithio amine having the general formula A 1  Li and from about 10 to about 90 parts by weight of at least one other lithio amine having the general formula A 2  Li. A 1  and A 2  are selected from the dialkyl, alkyl, cycloalkyl and dicycloalkyl amine radicals and cyclic amine radicals. There is also provided a method of forming a mixture of anionic polymerization initiators, a functionalized polymer and a method of forming a functionalized polymer.

This application is a division of application Ser. No. 08/220,629, filedMar. 30, 1994, now U.S. Pat. No. 5,578,542 which is a file wrappercontinuation of prior application Ser. No. 07/968,929, filed Oct. 30,1992, now abandoned.

TECHNICAL FIELD

The subject invention relates to anionic polymerization resulting indiene homo- and copolymer elastomers. More particularly, the presentinvention relates to polymerization employing soluble lithio amineinitiators. Specifically, the invention relates to an initiator which isa mixture of at least two different lithio amines, wherein their mixtureconfers solubility. The initiator is soluble in acyclic alkane solvents,and reproducibly polymerizes monomers in a controllable manner toproducts with a narrow molecular weight distribution range and otherdesirable properties.

BACKGROUND ART

When conducting polymerizations on a commercial basis, it is importantto utilize process conditions and components which will allow themolecular weight of the end products to be narrowly and reproduciblydefined. The characteristics of a given polymer and its usefulness aredependent, among other things, upon its molecular weight. Hence, it isdesirable to be able to predict with some certainty the molecular weightof the end product of the polymerization. When the molecular weight isnot narrowly definable, or is not reproducible on a systematic basis,the process may not be commercially viable.

In the art, it is desirable to produce elastomeric compounds exhibitingreduced hysteresis characteristics. Such elastomers, when compounded toform articles such as tires, power belts and the like, will show anincrease in rebound, a decrease in rolling resistance and will have lessheat build-up when subjected to mechanical stresses.

A major source of hysteretic power loss has been established to be dueto the section of the polymer chain from the last cross link of thevulcanizate to an end of the polymer chain. This free end cannot beinvolved in an efficient elastically recoverable process, and as aresult, any energy transmitted to this section of the cured sample islost as heat. It is known in the art that this type of heat loss can bereduced by preparing higher molecular weight polymers which necessarilyhave fewer end groups per given weight. However, this procedure is notalways useful because processability of the rubber with compoundingingredients and during shaping operations decreases rapidly withincreasing molecular weight.

U.S. Pat. No. 5,149,457 describes the use of mixtures of certain lithioamines to confer solubility in aromatic solvents. However, the use ofaromatic solvents is often undesirable for anionic polymerizations.Moreover, the lithium amides or lihio amines described in that patentare either unsuitable or undesirable as anionic polymerizationinitiators, or will not give products with reduced hysteresischaracteristics.

It is difficult to obtain consistent properties, such as a reduction inhysteresis characteristics, if the polymer cannot be controllablyreproduced in a narrow molecular weight distribution range. See, forexample, U.S. Pat. No. 4,935,471, in which some polymers are preparedwith a heterogeneous mixture of certain secondary amines, includinglithium pyrrolidide. Polymers made in this manner have widely varyingmolecular weights, broad polydispersities, and their functionalterminations tend to be erratic, giving rise to poorly reproduciblehysteresis reduction results.

A major drawback with many of these known anionic lithio amineinitiators, is that they are not soluble in acyclic alkanes, such ashexane. Polar solvents have heretofore been employed including the polarorganic compounds, especially ethers such as dimethyl or diethyl ether,as well as tetrahydrofuran, diethylene glycol methyl ether (diglyme).

The present invention provides novel, acyclic alkane soluble initiators,useful to initiate an anionic polymerization. The invention provides forthe incorporation of two separate functionalities from the initiator attwo or more ends of separate polymer chains. The invention also providesfor efficient, controllable and reproducible polymerizations, with thepreparation of well defined end-products of a relatively narrowmolecular weight distribution range and having desired hystereticproperties.

DISCLOSURE OF THE INVENTION

It is therefore, an object of the present invention to provide anionicpolymerization initiators which are soluble in acyclic alkanes.

It is a further object of the present invention to provide a method offorming a functionalized polymer from such an anionic polymerizationinitiator.

It is still a further object of the invention to provide an initiatorwhich will reproducibly polymerize a monomer or monomers within anarrow, predictable molecular weight range.

It is an additional object of the invention to provide such an initiatorwhich will allow for the incorporation of two separate functional groupsonto separate ends of the resulting polymers.

It is another object of the present invention to provide elastomersformed with such a polymerization initiator.

It is also an object of certain embodiments of the present invention toprovide diene polymers having reduced hysteresis characteristics.

It is a further object of the present invention to provide vulcanizableelastomeric compounds.

Still another object of the present invention is to provide an improvedtire formed at least in part, from an elastomer as above.

These and other objects together with the advantages thereof over theexisting art, which shall become apparent from the specification whichfollows, are accomplished by the invention as hereinafter described andclaimed.

In general, there is provided according to the invention, an acyclicalkane-soluble anionic polymerization initiator. The initiator consistsessentially of a mixture comprising from about 90 to about 10 parts byweight of a lithio amine having the general formula A₁ Li and from about10 to about 90 parts by weight of at least one other lithio amine havingthe general formula A₂ Li. The anionic radicals A₁ and A₂ are differentand each is selected from the group consisting of dialkyl, alkyl,cycloalkyl and dicycloalkyl amine radicals having the general formula##STR1## and cyclic amine radicals having the general formula ##STR2##where each R₁ is independently selected from the group consisting ofalkyls, cycloalkyls or aralkyls having from 1 to about 12 carbon atoms,and R₂ is selected from the group consisting of alkylene, oxy- oramino-alkylene groups having from about 3 to about 12 methylene groups.

There is also provided according to the invention, a method of forming afunctionalized polymer. The method comprises the steps of forming asolution of one or more anionically polymerizable monomers in an acyclicalkane solvent; and, polymerizing the monomers in the presence of aninitiator which is soluble in the acyclic alkane solvent. The initiatorconsists essentially of a mixture comprising from about 90 to about 10parts by weight of a lithio amine having the general formula A₁ Li andfrom about 10 to about 90 parts by weight of at least one other lithioamine having the general formula A₂ Li. A₁ and A₂ are as describedhereinabove.

A functionalized polymer according to the invention comprises a polymerhaving a functional group derived from a polymerization initiatorconsisting essentially of a mixture comprising from about 90 to about 10parts by weight of a lithio amine having the general formula A₁ Li andfrom about 10 to about 90 parts by weight of at least one other lithioamine having the general formula A₂ Li. A₁ and A₂ are as describedhereinabove.

There is also provided a method of preparing an acyclic alkane solubleanionic polymerization initiator, which comprises the steps of forming asolution of A₁ H and A₂ H in an anhydrous, aprotic solvent, where A₁ andA₂ are as described hereinabove; adding an organolithium compound to thesolution and allowing the organolithium compound to react with A₁ H andA₂ H. The organolithium compound has the general formula RLi where R isselected from the group consisting of alkyls, cycloalkyls, alkenyls,aryls and aralkyls having from 1 to about 20 carbon atoms and shortchain length low molecular weight polymers from diolefin and vinyl arylmonomers having up to about 25 units.

PREFERRED EMBODIMENTS FOR CARRYING OUT THE INVENTION

As will become apparent from the description which follows, the presentinvention provides novel polymerization initiators which are mixturessoluble in acyclic alkanes such as hexane, pentane, heptane, octane,their alkylated derivatives, mixtures thereof and the like. A initiatoris considered to be soluble herein if it is soluble up to about 1 molarconcentration at room temperature, as demonstrated by a lack ofobservable precipitate. Some useful initiators according to theinvention are soluble at lower and some at higher concentrations. It hasalso been discovered herein that certain vulcanizable elastomericcompounds and articles thereof based upon functionalized polymers formedusing such an initiator mixture, exhibit useful properties, such as forexample, reproducible relatively narrow molecular weight ranges.Furthermore, each of the resulting polymers contains a functionalityfrom one of the components of the initiators, which functionality isuseful for example, in improving hysteresis properties, that is,reducing hysteretic loss.

While the initiators of the present invention are soluble in acyclicalkane solvents, it will be appreciated that the use of the initiatorsin other solvent systems is also within the scope of the invention, aswill be further described hereinbelow.

The initiator according to the invention preferably consists essentiallyof a metal amide which may or may not be soluble in an acyclic alkanesolvent, and one or more other metal amides which also may Or may not besoluble in an acyclic alkane solvent. Preferably, the metal amides arelithium amides (also called lithio amines), and the present inventionwill be exemplified hereinbelow with respect to lithium, it beingunderstood that other metal amides are within the scope of theinvention.

The initiator has the general formula xA₁ Li.yA₂ Li, where x+y=1 andboth x and y range from about 0.1 to about 0.9, and preferably from 0.3to about 0.7. That is, in the broad embodiment, the initiator containsfrom about 90 to about 10 parts by weight of A₁ Li and from about 10 toabout 90 parts by weight of A₂ Li.

The A₁ and A₂ components in each of the amines of the initiator,represent an amine functionality to be incorporated into the resultingpolymer. For example, A₁ and A₂ may be selected from the groupconsisting of dialkyl, alkyl, cycloalkyl and dicycloalkyl amine radicalshaving the general formula ##STR3## and cyclic amine radicals having thegeneral formula ##STR4## Each R₁ is independently selected from thegroup consisting of alkyls, cycloalkyls or aralkyls having from 1 toabout 12 carbon atoms, and R₂ is selected from the group consisting ofan alkylene, oxy- or amino-alkylene group having from about 3 to about12 methylene groups.

Exemplary R₁ groups include methyl, ethyl, butyl, octyl, cyclohexyl,3-phenyl-1-propyl, isobutyl and the like. Exemplary R₂ groups includetetramethylene, hexamethylene, oxydiethylene, N-alkylazadiethylene andthe like. R₂ may be bicyclic, such that two methylene groups therein arebridged to form a bicycloalkane, such as 1,3,3-trimethyl-6-azabicyclo3.2.1!octane. By "bridged" it is understood to mean that twonon-adjacent methylene groups in a larger ring are connected, either bybonding directly or through an alkylene group having one or moremethylene groups, thus forming a bicyclic structure of smaller rings.

It has been found that when one or both R1 and R₂ are both t-butylgroups, both isopropyl groups or the like, the resulting polymerizationsare slow, presumably due to hindrance around the nitrogen at theinitiation site. Hence, in a preferred embodiment of the invention, thecarbon atoms in R₁ and R₂ bonded directly to the nitrogen in the amineradical, are also bonded to at total of at least three hydrogen atoms.

For example, as long as A₁ and A₂ are different they may each be aderivative of pyrrolidine; piperidine; piperazine; perhydroazepine, alsoknown as hexamethyleneimine (HMI); 3,3,5-trimethyltetrahydroazepine,also known as trimethylhexamethyleneimine (THMI); and, 1-azacyclooctaneincluding bicyclics such as perhydroisoquinoline, perhydroundole, andthe like. A₁ and A₂ may each also be derived from di-n-propylamine,diisobutylamine, ethylamine, or n-butylamine. Pyrrolidine,perhydroazepine and 1-azacyclooctane are preferred for forming the metalamides in the mixture.

Preferred A₁ and A₂ components for the amine precursor of the metalamides include hexamethyleneimine, 1,3,3-trimethyl-6-azabicyclo 3.2.1!octane, diisobutyl amine, pyrrolidine, 1-azacyclooctane,3,3,5-trimethyltetrahydroazepine.

As stated hereinabove, some of the metal amides may not each bethemselves soluble (as the term is used herein) in acyclic alkanes. Forexample, lithium pyrrolidide, lithium hexamethyleneimine and lithiumazacyclooctane are not soluble in hexane, while lithium diisobutylamideis soluble in hexane. One of the unexpected results of the invention, isthat such otherwise non-soluble metal amides are rendered soluble whenmixed with other metal amides, as will be exemplified hereinbelow.

The initiator according to the present invention can be formed bypreparing a mixture of the amine components A₁ H and A₂ H, in ananhydrous, aprotic solvent, such as the hexane. To this solution is thenadded an organolithium reagent in the same or a similar solvent. Thatis, an acyclic alkane soluble mixture of anionic polymerizationinitiators is prepared, according to one aspect of the invention, byforming a solution of a first functionalizing agent and at least oneother functionalizing agent in an anhydrous, aprotic solvent, and addingan organolithium reagent to the solution. The organolithium reagent hasthe general formula RLi where R is selected from the group consisting ofalkyls, cycloalkyls, alkenyls, aryls and aralkyls having from 1 to about20 carbon atoms and short chain length low molecular weight polymersfrom diolefin and vinyl aryl monomers having up to about 25 units.Typical alkyls include n-butyl, s-butyl, methyl, ethyl, isopropyl andthe like. The cycloalkyls include cyclohexyl, menthyl and the like. Thealkenyls include allyl, vinyl and the like. The aryl and aralkyl groupsinclude phenyl, benzyl, oligo(styryl) and the like. Exemplary shortchain length polymers, also known as "oligomers", include theoligo(butadienyls), oligo(isoprenyls), oligo(styryls) and the like.

The solution of the mixture of amines and the organolithium reagent isallowed to react for from several minutes to 1 to 2 hours or more atambient temperature (25° to 30° C.), or elevated temperatures up toabout 100° C., preferably at less than 50° C., and more preferably atless than 38° C., following which the soluble catalyst is ready for use.Reaction times of about one hour are normally sufficient.

The two amide initiators are mixed in amounts of from about 90 to about10 parts by weight of the first amide component with from about 10 toabout 90 parts by weight of the second amide component. It is preferredthat the two amides be mixed at a ratio of from about 30:70 to about70:30 parts by weight, and more preferably at about 50:50 parts byweight. The amide components are mixed in an excess of an acyclic alkaneor hydrocarbon solvent. If more than one second amide component is used,the ratios may be adjusted accordingly. The final concentration of mixedlithium amides may range from very dilute to as high as 1 or 2 molar,depending on the combination of amides used.

As stated above, the initiator mixture thus formed may be employed as toprepare many anionically-polymerized elastomers, e.g., polybutadiene,polyisoprene and the like, and copolymers thereof with monovinylaromatics such as styrene, alpha methyl styrene and the like, or trienessuch as myrcene. Thus, the elastomers include diene homopolymers andcopolymers thereof with monovinyl aromatic polymers. Suitable monomersinclude conjugated dienes having from about 4 to about 12 carbon atomsand monovinyl aromatic monomers having 8 to 18 carbon atoms and trienes.Examples of conjugated diene monomers and the like useful in the presentinvention include 1,3-butadiene, isoprene, 1,3-pentadiene,2,3-dimethyl-1,3-butadiene and 1,3-hexadiene, and aromatic vinylmonomers include styrene, a-methylstyrene, p-methylstyrene, vinyltolueneand vinylnaphtalene. The conjugated diene monomer and aromatic vinylmonomer are normally used at the weight ratios of 95-50:5-50, preferably95-65:5-35.

Polymerization is conducted in an acyclic alkane or hydrocarbon solvent,such as the various pentanes, hexanes, heptanes, octanes, theiralkylated derivatives, and mixtures thereof. Other solvents may also beused, including cyclohexane, benzene and the like. In order to promoterandomization in copolymerization and to control vinyl content, a polarcoordinator may be added to the polymerization ingredients. Amountsrange between 0 and 90 or more equivalents per equivalent of lithium.The amount depends on the amount of vinyl desired, the level of styreneemployed and the temperature of the polymerization, as well as thenature of the specific polar coordinator (modifier) employed.

Compounds useful as polar coordinators are organic and includetetrahydrofuran, linear and cyclic oligomeric oxolanyl alkanes such as2-2'-di(tetrahydrofuryl) propane, di-piperidyl ethane,hexamethylphosphoramide, N-N'-dimethylpiperazine, diazabicyclooctane,dimethyl ether, diethyl ether, tributylamine and the like. The linearand cyclic oligomeric oxolanyl alkane modifiers are described in U.S.Pat. No. 4,429,091, the subject matter of which is incorporated hereinby reference. Compounds useful as polar coordinators include thosehaving an oxygen or nitrogen hetero-atom and a non-bonded pair ofelectrons. Other examples include dialkyl ethers of mono and oligoalkylene glycols; "crown" ethers; tertiary amines such astetramethylethylene diamine (TMEDA); linear THF oligomers and the like.

A batch polymerization is prepared by conventional techniques, and maybe begun by charging a blend of monomer(s) and acyclic alkane solvent orother appropriate solvents, to a suitable reaction vessel, followed bythe addition of the polar coordinator (if employed) and the mixture ofinitiator compounds previously described. The reactants are heated to atemperature of from about 20° to about 200° C., and the polymerizationis allowed to proceed for from about 0.1 to about 24 hours. A functionalamine group is derived from each of the initiator compounds and bonds atthe initiation site of one of the growing polymers. Thus, substantiallyevery resulting polymer chain has the general formula A₁ YLi or A₂ YLiwhere A₁ and A₂ are as described above, and Y is a divalent polymerradical which is derived from any of the foregoing diene homopolymers,monovinyl aromatic polymers, diene/monovinyl aromatic random copolymersand block copolymers. The monomer addition at the lithium end causes themolecular weight of the polymer to increase as the polymerizationcontinues.

To terminate the polymerization, and thus further control polymermolecular weight, a polymer modifying agent such as a terminating,coupling or linking agent may be employed. Useful modifying agentsinclude active hydrogen compounds such as water or alcohol, or compoundsproviding multifunctionality such as, for example, carbon dioxide;tetramethyldiaminobenzophenone; dialkyl- and dicycloalkyl-carbodiimideshaving from about 5 to about 20 carbon atoms; (R₃)_(a) ZX_(b) ; ##STR5##where Z is tin or silicon. It is preferred that Z is tin.

R₃ is an alkyl having from about 1 to about 20 carbon atoms; acycloalkyl having from about 3 to about 20 carbon atoms; an aryl havingfrom about 6 to about 20 carbon atoms; or, an aralkyl having from about7 to about 20 carbon atoms. For example, R₃ may include methyl, ethyl,n-butyl, neophyl, phenyl, cyclohexyl or the like.

X is chlorine, bromine or iodine, "a" is from 0 to 3, and "b" is from 1to 4; where a+b=4.

Each R₄ is the same or different and is an alkyl, cycloalkyl or aryl,having from about 1 to about 12 carbon atoms. For example, R₄ mayinclude methyl, ethyl, nonyl, t-butyl, phenyl or the like.

R₅ is an alkyl, phenyl, alkylphenyl or dialkylaminophenyl, having fromabout 1 to about 20 carbon atoms. For example, R₅ may include t-butyl,2-methyl-4-pentene-2-yl, phenyl, p-tolyl, p-butylphenyl,p-dodecylphenyl, p-diethyl-aminophenyl, p-(pyrrolidino)phenyl, and thelike.

Each R₆ is the same or different, and is an alkyl or cycloalkyl havingfrom about 1 to about 12 carbon atoms. Two of the R₆ groups may togetherform a cyclic group. For example, R₆ may include methyl, ethyl, octyl,tetramethylene, pentamethylene, cyclohexyl or the like.

R₇ may include alkyl, phenyl, alkylphenyl or dialkylaminophenyl, havingfrom about 1 to about 20 carbon atoms. For example, R₇ may includemethyl, butyl, phenyl, p-butylphenyl, p-nonylphenyl,p-dimethylaminophenyl, p-diethylaminophenyl, p-(piperidino)phenyl, orthe like.

Other examples of useful modifying agents include SnCl₄, (R₁)₃ SnCl,(R₁)₂ SnCl₂, R₁ SnCl₃, SiCl₄, (R₁)₃ SiCl, (R₁)₂ SiCl₂, R₁ SiCl₃,carbodiimides, N-methylpyrrolidine, cyclic amides, cyclic ureas,isocyanates, Schiff bases, 4,4'-bis(diethylamino) benzophenone, and thelike, where R₁ is as described hereinabove.

The modifying agent is added to the reaction vessel, and the vessel isagitated for about 1 to about 1000 minutes. As a result, an elastomer isproduced having an even greater affinity for compounding materials suchas carbon black, and hence, even further reduced hysteresis. Additionalexamples of modifying agents include those found in U.S. Pat. No.4,616,069 which is herein incorporated by reference. Care should betaken to preserve the live C-Li for effective termination, such as byavoiding prolonged exposure to high temperatures or impurities such asprotic acids or the like.

The polymer may be separated from the solvent by conventionaltechniques. These include steam or alcohol coagulation, thermaldesolventization, or any other suitable method. Additionally, solventmay be removed from the resulting polymer by drum drying, extruderdrying, vacuum drying or the like.

The elastomers of the present invention comprise a plurality of polymermolecules having a functional group at two or more ends. Compounds ofsuch polymers may result in products exhibiting reduced hysteresis,which means a product having increased rebound, decreased rollingresistance and has less heat build-up when subjected to mechanicalstress. Furthermore, one aspect according to the invention elastomer isformed from a plurality of polymer chains as above, and is alsomultifunctional wherein the polymer also carries a tin-carbon bond, suchas may be derived from a modifying agent such as the terminating,coupling or linking agent discussed hereinabove.

It has also been found, as will be exemplified hereinbelow, thatpolymers formed using the initiator mixture of the invention, arerepeatably producible in a relatively narrow range of molecular weights,such as that substantially consistently reproducible polymers arepossible with a molecular weight range of about 20,000 to about 250,000.

The polymers of the present invention can be used alone or incombination with other elastomers to prepare an elastomer product suchas a treadstock compound. A treadstock compound can be formed from avulcanizable elastomeric composition of the invention polymers. A tireaccording to the invention may have at least a portion of its treadformed from such a treadstock compound. Compounds to form other tirestructural elements, such as sidewalls, carcasses and the like, can alsobe advantageously made from the polymers of the present invention.

For example, the polymers according to the invention can be blended withany conventionally employed treadstock rubber which includes naturalrubber, synthetic rubber and blends thereof. Such rubbers are well knownto those skilled in the art and include synthetic polyisoprene rubber,styrene/butadiene rubber (SBR), polybutadiene, butyl rubber, Neoprene,ethylene/propylene rubber, ethylene/propylene/diene rubber (EPDM),acrylonitrile/butadiene rubber (NBR), silicone rubber, thefluoroelastomers, ethylene acrylic rubber, ethylene vinyl acetatecopolymer (EVA), epichlorohydrin rubbers, chlorinated polyethylenerubbers, chlorosulfonated polyethylene rubbers, hydrogenated nitrilerubber, tetrafluoroethylene/propylene rubber and the like. When thepolymers of the present invention are blended with such conventionalrubbers, the amounts can vary widely such as between 10 and 99 percentby weight.

The polymers can be compounded with reinforcing agents such as carbonblack in amounts ranging from about 5 to about 100 parts by weight, per100 parts of rubber (phr), with about 5 to about 80 phr being preferred,in order to form a vulcanizable elastomeric composition. Useful carbonblacks may include any of the commonly available, commercially-producedcarbon blacks but those having a surface area (EMSA) of at least 20 m²/gram and more typically at least 35 m² /gram up to 200 m² /gram orhigher are preferred. Surface area values used in this application arethose determined by ASTM test D-1765 using the cetyltrimethyl-ammoniumbromide (CTAB) technique. Among the useful carbon blacks are furnaceblack, channel blacks and lamp blacks. More specifically, examples ofthe carbon blacks include super abrasion furnace (SAF) blacks, highabrasion furnace (HAF) blacks, fast extrusion furnace (FEF) blacks, finefurnace (FF) blacks, intermediate super abrasion furnace (ISAF) blacks,semi-reinforcing furnace (SRF) blacks, medium processing channel blacks,hard processing channel blacks and conducting channel blacks. Othercarbon blacks which may be utilized include acetylene blacks. Mixturesof two or more of the above blacks can be used in preparing the carbonblack products of the invention. Typical values for surface areas ofusable carbon blacks are summarized in the following TABLE I.

                  TABLE I                                                         ______________________________________                                        CARBON BLACKS                                                                 ASTM           Surface Area                                                   Designation    m.sup.2 /g                                                     (D-1765-82a)   (D-3765)                                                       ______________________________________                                        N-110          126                                                            N-220          111                                                            N-339          95                                                             N-330          83                                                             N-550          42                                                             N-660          35                                                             ______________________________________                                    

The carbon blacks utilized in the preparation of the rubber compounds ofthe invention may be in pelletized form or an unpelletized flocculentmass. Preferably, for more uniform mixing, unpelletized carbon black ispreferred. The reinforced rubber compounds can be cured in aconventional manner with known vulcanizing agents at about 0.5 to about4 phr. For example, sulfur or peroxide-based curing systems may beemployed. For a general disclosure of suitable vulcanizing agents onecan refer to Kirk-Othmer, Encyclopedia of Chemical Technology, 3rd ed.,Wiley Interscience, N.Y. 1982, Vol. 20, pp. 365-468, particularly"Vulcanization Agents and Auxiliary Materials" pp. 390-402. Vulcanizingagents may be used alone or in combination.

Vulcanizable elastomeric compositions of the invention can be preparedby compounding or mixing the polymers thereof with carbon black andother conventional rubber additives such as fillers, plasticizers,antioxidants, curing agents and the like, using standard rubber mixingequipment and procedures and conventional amounts of such additives.

General Experimental

In order to demonstrate the preparation and properties of the initiatormixture and elastomers of the present invention, a number of suchinitiator mixtures and elastomers were prepared. A solution of styreneand butadiene monomers in hexane was prepared and polymerized with theabove described mixtures. As noted above, various techniques known inthe art for carrying out anionic polymerizations may be employed withoutdeparting from the scope of the present invention.

EXAMPLE NO. 1 Preparation of Initiator Mixture

3,3,5-trimethyltetrahydroazepine (also known astrimethylhexamethyleneimine or "THMI"), was vacuum distilled fromcalcium hydride at approximately 75° C. at approximately 15 Torr andtransferred under nitrogen to a dried, nitrogen-purged bottle.Hexamethyleneimine, "HMI", was distilled from calcium hydride andtransferred under nitrogen to a dried, nitrogen-purged bottle. The mixedlithium amides HMI and THMI ("LHMI/LTHMI") were prepared by treating amixture of 7.5 milli equivalent (meq) of a 1.16M solution of THMI inhexanes and 7.5 meq of neat HMI with 15.0 meq of a 1.67M solution ofn-butyllithium in hexanes, swirling the mixture at room temperatureovernight. The resulting approximately 0.9M solution was a clear, paleyellow. When either HMI or THMI alone was treated with n-butyllithium inhexanes in the absence of the second amine, cloudiness and/orprecipitation occurred immediately. The ("LHMI/LTHMI") solution wasstable for at least a month at room temperature. Samples were drawn fromit by syringe for use in initiating polymerization.

A. Polymerization of Butadiene and Styrene with LIIMI/LTIIMI:

A 0.9M solution of the above initiator mixture was added to a 80percent/20 percent by weight blend of butadiene and styrene in hexanes,at a level of 1.0 meq Li/100 g monomer, andN,N,N',N'-tetramethylethylenediamine ("TMEDA") was added at 0.30TMEDA/Li on a mole/mole basis. The mixture was agitated at 50° C. for2.5 hr, proceeding to approximately 100 percent conversion to polymer.In practicing the invention, there is considerable leeway in thereaction times and temperatures, as well as in the reaction vessels,type of agitation, etc., used. The polymer cements then were quenched byinjection with 1.5 ml of i-PrOH, treated with an antioxidant (3 ml of amixture containing 1.6 wt percent DBPC in hexane), coagulated in i-PrOH,air-dried at room temperature, then drum-dried. Suitablecharacterizations were performed. The product polymer contained 20.0percent styrene (1.5 percent block), 37.0 percent vinyl (46.3 percentvinyl if butadiene (or "BD")=100 percent), Tg -47° C., GPC(THF): M_(n)103582, molecular weight distribution (Mw/Mn or MWD) 1.31, rawML/4/100=15.

B. Polymerization of Butadiene and Styrene with LIIMI/LTIIMI andEnd-linking with SnCl₄ :

The above procedure was followed exactly, except that after 1.5 hour ofpolymerization at 50° C., the polymerization mixture was treated with0.8 equivalent of SnCl₄ per equivalent of Li charged. The product wasworked up in the same manner as above. The product polymer contained19.4 percent styrene (0.8 percent block), 39.5 percent vinyl (49 percentvinyl if BD=100 percent), Tg -45° C., GPC(THF): M_(n) 165756, MWD 1.72,ca. 54 percent high molecular weight; raw ML/4/100=65.

Evaluation of Compounded Properties

The product polymer was compounded and tested as indicated in the testrecipe shown in TABLE II, and cured 20 minutes at 165° C. Results ofphysical tests are reported in TABLE III hereinbelow:

                  TABLE II                                                        ______________________________________                                        COMPOUNDING RECIPE                                                                        Mix    Parts per Hundred                                          Ingredient  Order  Parts Rubber                                               ______________________________________                                        Polymer     1      100         Masterbatch                                    Naphthenic oil                                                                            2      10          145-155° C., 60 RPM                     Carbon black, N-351                                                                       3      55                                                         ZnO         4      3                                                          Antioxidant 5      1                                                          Wax blend   6      2                                                          Total Masterbatch: 171                                                        Stearic acid       2           Final                                          Sulfur             1.5         77-93° C., 40 RPM                       Accelerator        1                                                          TotaI Final:       175.5                                                      ______________________________________                                    

                  TABLE III                                                       ______________________________________                                        PHYSICAL TEST RESULTS, EXAMPLE NO. 1                                                       1 Hz Dynastat                                                                          Ring Stress-Strain, R.T.                                ML/4/212       tan δ             Percent                                Example No.                                                                           (gum)   (cpd)  50° C.                                                                          M300 T.S.  Eb                                 ______________________________________                                        1-A     15      65     0.098    2562 3244  410                                1-B     65      94     0.088    2673 3167  390                                ______________________________________                                    

In addition, the carbon-bound rubber content of the uncured, finalcompounded stocks of 1-A and 1-B were 36 percent and 42 percentrespectively. This indicates an enhanced interaction between the polymerand carbon black in these cases, compared to unmodified rubber, whichtypically exhibits 20-22 percent carbon-bound rubber, and a comparablebutyllithium-initiated, Sn-linked rubber, which typically exhibits 31-33percent carbon-bound rubber. The results of this test provide goodevidence for reduced hysteresis in this polymer. The Dynastat tan δ(50°C.)=0.098 is about 50 percent below the value expected for a comparableunmodified polymer of this molecular weight, prepared using a typicalalkyllithium initiator.

The carbon-bound rubber content was determined by placing a 0.4 to 0.5grams sample of the uncured compound into 100 ml of distilled reagenttoluene for two days at room temperature and without agitation. Afterrecovering the solids, at constant weight the amount of rubber attachedto carbon can be estimated since the amount of other insolubleingredients in the original sample, (such as the carbon black) areknown.

EXAMPLE NO. 2 Preparation or Initiator Mixture

Hexamethyleneimine, "HMI", was distilled and handled as described above.Pyrrolidine, "PY", was distilled from CaH₂ at atmospheric pressure andhandled in the same manner. The mixed N-lithio salts of HMI and PY("LHMI/LPY") were prepared by treating a mixture of 7.5 meq of a 5.45Msolution of PY in hexanes and 7.5 meq of a 2.24M solution of HMI in85:15 cyclohexane: hexanes with 15.0 meq of a 1.67M solution ofn-butyllithium in hexanes, swirling the mixture at room temperatureovernight. The resulting ˜1.09M solution was a clear, light-mediumyellow. When PY alone was treated with n-butyllithium in hexane orcyclohexane, in the absence of the second amine or other solubilizationagent, heavy precipitation occurred almost immediately. The ("LHMI/LPY")solution was stable for at least several days at room temperature.Samples were drawn from it by syringe for use in initiatingpolymerization.

A. Polymerization of Butadiene and Styrene with LIIMI/LPY:

The 1.09M solution of the above initiator was added to a 80 percent/20percent by weight blend of butadiene and styrene in hexanes, at a levelof 1.0 meq Li/100 g monomer, and TMEDA was added at 0.30 TMEDA/Li. The,mixture was agitated at 50° C. for 2.5 hours, proceeding toapproximately 100 percent conversion to polymer. The polymer was workedup as described in the previous examples. The product polymer contained20.2 percent styrene (3.3 percent block), 28.7 percent vinyl (36.0percent vinyl if BD=100 percent), Tg -58° C., GPC(THF): M_(n) 103302,MWD 1.60, raw ML/4/100=21.

B. Polymerization of Butadiene and Styrene with LHMI/LPY and End-linkingwith SnCl₄ :

The above procedure was followed exactly, except that after 1.5 hour ofpolymerization at 50° C., the polymerization mixture was treated with0.8 equivalents of SnCl₄ per equivalents of Li charged. The product wasworked up in the same manner as above. The product polymer contained20.1 percent styrene (1.6 percent block), 35.0 percent vinyl (43.8percent vinyl if BD=100 percent), Tg -49° C., GPC(THF): M_(n) 145511,MWD 1.90, ca. 52 percent high molecular weight; raw ML/4/100=62.

Evaluation of Compounded Properties:

Product polymer 2-B was compounded and tested as indicated in the testrecipe shown in TABLE II hereinabove, and cured 20 minutes at 165° C.Results of physical tests are reported in TABLE IV hereinbelow.

                  TABLE IV                                                        ______________________________________                                        PHYSICAL TEST RESULTS, EXAMPLE No. 2                                                       1 Hz Dynastat                                                                          Ring Stress-Strain, R.T.                                ML/4/212       tan δ       Percent                                      Example No.                                                                           (gum)   (cpd)  50° C.                                                                          M300 T.S.  Eb                                 ______________________________________                                        2-B     62      98     0.101    2996 3893  411                                ______________________________________                                    

The results of this test provided good evidence for reduced hysteresisin this polymer. The Dynastat tan δ(50° C.)=0.101 is about 48 percentbelow the value expected for an unmodified polymer of this molecularweight, prepared using a typical alkyllithium initiator.

A preferred method of preparing the initiators for the mixture,according to the invention, is as follows. A glass vessel, such as asmall bottle containing a Teflon or glass-clad magnetic stirring bar, isdried, sealed, and purged with nitrogen. The following reagents areadded at room temperature by syringe while stirring:

1. 30 mmol total of a mixture of anhydrous secondary amines inhydrocarbon solvent;

2. 30.1 mmol of alkyl lithium in hydrocarbon solvent (added by syringeat once, with stirring, while taking precaution for back-pressures).

The solution will heat and develop pressure immediately, but will soonbegin to cool back down. When larger amounts of reagent are prepared,e.g. 250-300 mmol in large bottles or 0.5-1.5 mol in reactors, bestresults are obtained when chilled or cold water cooling is used to keepthe peak reaction temperature at about 38° C. or below. The normalprocedure has been to allow the mixture to stir overnight at roomtemperature before using. However, the reaction is essentially completewithin minutes. The mixture should be clear, straw-yellow, withoutsignificant precipitation. Light-to-moderate haziness or cloudiness doesnot appear to affect activity. Anhydrous conditions are required.Hydrocarbon solvent solutions with less than 30 parts per million (ppm)of water give best results. Some solutions are stable for 3 or moredays, and initiator reagents can be stored under positive nitrogenpressures for periods of up to several weeks or more at room temperature(25°-27° C.).

As is clear from the foregoing examples and specification disclosure,that initiator mixtures according to the present invention are usefulfor the anionic polymerization of diene monomers. Reproduciblepolymerization of such polymers within a relatively narrow molecularweight range is achieved, and the resulting polymers also exhibit goodpreservation of live C-Li ends, when compared to the initiatorsheretofore known in the art.

It is to be understood that the invention is not limited to the specificinitiator reactants, monomers, modifying agents, polar coordinators orsolvents disclosed herein, except as otherwise stated in thespecification. Similarly, the examples have been provided merely todemonstrate practice of the subject invention and do not constitutelimitations of the invention. Those skilled in the art may readilyselect other monomers and process conditions, according to thedisclosure made hereinabove.

Thus, it is believed that any of the variables disclosed herein canreadily be determined and controlled without departing from the scope ofthe invention herein disclosed and described. Moreover, the scope of theinvention shall include all modifications and variations that fallwithin the scope of the attached claims.

What is claimed is:
 1. A method of forming a functionalized polymer, comprising the steps of:forming a solution of one or more anionically polymerizable monomers in an acyclic alkane solvent; and, polymerizing said monomers in the presence of an initiator which is soluble in said acyclic alkane solvent; said initiator consisting essentially of a mixture comprising: from about 90 to about 10 parts by weight of a lithio amine having the formula A₁ Li and from about 10 to about 90 parts by weight of at least one other lithio amine having the formula A₂ Li; wherein A₁ and A₂ are different and independently selected from the group consisting of dialkyl, alkyl, cycloalkyl, aralkyl and dicycloalkyl amine radicals having the formula ##STR6## and cyclic amine radicals having the formula ##STR7## where each R₁ is independently selected from the group consisting of alkyls, cycloalkyls or aralkyls having from 1 to about 12 carbon atoms, and R₂ is selected from the group consisting of an alkylene, oxy- or amino-alkylene group having from about 3 to about 12 methylene groups.
 2. A method, as set forth in claim 1, comprising the further step of reacting the polymer with a modifying agent, such that the resulting polymer is multifunctional.
 3. A method, as set forth in claim 2, wherein said modifying agent is selected from the group consisting of carbon dioxide; tetramethyldiaminobenzophenone; dialkyl- and dicycloalkyl-carbodiimides having from about 5 to about 20 carbon atoms; (R₃)_(a) ZX_(b) ; ##STR8## where Z is tin or silicon; R₃ is selected from the group consisting of alkyls having from 1 to about 20 carbon atoms, cycloalkyls having from about 3 to about 20 carbon atoms, aryls having from about 6 to about 20 carbon atoms and aralkyls having from about 7 to about 20 carbon atoms; X is chlorine or bromine; a is an integer of from 0 to 3, and b is an integer of from 1 to 4, where a+b=4; each R₄ is the same or different and is selected from the group consisting of alkyls, cycloalkyls and aryls, having from 1 to about 12 carbon atoms; R₅ is selected from the group consisting of alkyls, phenyls, alkylphenyls and dialkylaminophenyls, having from 1 to about 20 carbon atoms; and, each R₆ is the same or different, and is selected from the group consisting of alkyls and cycloalkyls having from 1 to about 12 carbon atoms.
 4. A method, as set forth in claim 3, wherein the two R₆ groups together form a cyclic group.
 5. A method, as set forth in claim 1, wherein said one or more anionically polymerizable monomers are selected from the group consisting of conjugated dienes having from about 4 to about 12 carbon atoms and monovinyl aromatic monomers having 8 to 18 carbon atoms and trienes.
 6. A functionalized polymer according to the method as set forth in claim
 1. 7. An elastomer comprising a plurality of polymer chains of the functionalized polymer set forth in claim
 6. 8. An elastomer, as set forth in claim 7, wherein a plurality of said polymer chains also carry at least one tin-carbon bond.
 9. A rubber composition formed from the elastomer of claim 8 and from about from about 5 to about 80 parts by weight of carbon black, per 100 parts of the elastomer.
 10. A treadstock compound formed from the rubber composition of claim
 9. 11. A tire having at least one component formed from the rubber composition of claim
 9. 12. A method of forming a functionalized polymer, comprising the steps of:forming a solution of one or more anionically polymerizable monomers in an acyclic alkane solvent; and, polymerizing said monomers in the presence of an initiator which is soluble in said acyclic alkane solvent; said initiator consisting essentially of a mixture comprising: from about 90 to about 10 parts by weight of a lithio amine having the formula A₁ Li and from about 10 to about 90 parts by weight of at least one other lithio amine having the formula A₂ Li; wherein A₁ and A₂ are different and independently selected from the group consisting of cyclic amine radicals having the formula ##STR9## where each R₂ is selected from the group consisting of an alkylene, oxy- or amino-alkylene group having from about 3 to about 12 methylene groups.
 13. A method, as set forth in claim 12, comprising the further step of reacting the polymer with a modifying agent, such that the resulting polymer is multifunctional.
 14. A method, as set forth in claim 13, wherein said modifying agent is selected from the group consisting of carbon dioxide; tetramethyldiaminobenzophenone; dialkyl- and dicycloalkyl-carbodiimides having from about 5 to about 20 carbon atoms; (R₃)_(a) ZX_(b) ; ##STR10## where Z is tin or silicon; R₃ is selected from the group consisting of alkyls having from 1 to about 20 carbon atoms, cycloalkyls having from about 3 to about 20 carbon atoms, aryls having from about 6 to about 20 carbon atoms and aralkyls having from about 7 to about 20 carbon atoms; X is chlorine or bromine; a is an integer of from 0 to 3, and b is an integer of from 1 to 4, where a+b=4; each R₄ is the same or different and is selected from the group consisting of alkyls, cycloalkyls and aryls, having from 1 to about 12 carbon atoms; R₅ is selected from the group consisting of alkyls, phenyls, alkylphenyls and dialkylaminophenyls, having from 1 to about 20 carbon atoms; and, each R₆ is the same or different, and is selected from the group consisting of alkyls and cycloalkyls having from 1 to about 12 carbon atoms.
 15. A method, as set forth in claim 14, wherein the two R₆ groups together form a cyclic group.
 16. A method, as set forth in claim 12, wherein said one or more anionically polymerizable monomers are selected from the group consisting of conjugated dienes having from about 4 to about 12 carbon atoms and monovinyl aromatic monomers having 8 to 18 carbon atoms and trienes. 